Phonemes are the basic unit of speech. They are the simplest speech sounds that are used to differentiate between one word and another. A phoneme is capable of creating distinctions in meaning between words.
Pragmatics is the study of the social use of language. It examines how people understand and produce communicative acts in real world situations. Speakers will style shift depending on the context of their talk. The form of utterances can be varied by altering morphology, syntax, vocabulary and phonology. The ability to consciously shift the style of speaking to suit the occasion is important in social contexts. This ability may be reduced in people with communication difficulties.
Morphology studies the internal structure of words and their alteration through the combination of morphemes. A morpheme is the smallest element in a language capable of creating a distinction in meaning. There are bound morphemes (e.g. -s, -ed, -ing) and free morphemes (e.g. go, stop, run).
Semantics is the study of the meaning of linguistic tokens such as words, phrases and clauses. It examines which signs are used, how they make reference to things, ideas, emotions, and so on, and how the hearer interprets them.